The present invention relates to a storage device and control method for the storage device, and is particularly suited for use in a storage device that performs processing for writing discontinuous data to a physical disk.
Conventionally, data write processing to a physical disk in a storage device is largely divided into random write, i.e., processing for writing discontinuous data to a physical disk, and sequential write, i.e., processing for writing continuous data to a physical disk.
Because data transfer performance during sequential write is far greater than during random write in general, data writing to a physical disk can be performed at high speed during sequential write.
As a method for improving random write performance, data write processing in log format (hereinafter referred to as “log format-write”), in which discontinuous data is address-converted in a storage control unit in a storage device and the address-converted data is used as continuous data, has been proposed (see U.S. Pat. No. 6,516,380 B2). A storage device that employs log format-writing has a primary volume, which is a physical disk area for storing usual data, and a log volume for storing data with sequential-converted addresses.
However, the log volume is limited in log format-writing. Therefore, when the available log volume capacity becomes small, processing (hereinafter referred to as “log clearance processing”) for clearing the log volume and address conversion table by transferring data in the log volume to the primary volume is necessary.
Moreover, when executing log clearance processing during log format-writing, random write based on data write to the primary volume, which is relevant to normal access to disks performed during non-log format-writing, is always necessary.
Accordingly, when executing log clearance processing in log format-writing, random write for clearing the log volume also has to be performed in the sequential write to the log volume. The random write processing efficiency is then reduced, which obstructs speeding up of the log format-writing.